Unreasonable customers are always a pain, but they're especially prevalent and stressful during the holiday shopping rush. Just ask Anton Skorucak, founder and CEO of xUmp.com, an online retailer of scientific educational supplies, toys and gifts. The company used to give customers a choice between ground and next-day air shipping on holiday orders. Often, they would choose the cheapest option, ignoring the details and later accusing the company of "ruining their Christmas" because their package didn't arrive by December 24.

To try to eliminate such frustrating experiences, xUmp last year launched a "Guaranteed in time for Christmas" shipping offer. When customers choose this option, the onus falls on xUmp to select the shipping method that will ensure the package arrives in time. The company adjusts the cost of this option daily, with the price increasing as Christmas Day draws closer. "I am happy to report that last year as a result of this, we did not ruin anyone's Christmas," Skorucak says.

To help you cope with difficult shoppers this holiday season, consider these five tips from customer-service experts:

1. Remember: The customer is always right.
The old "customer is always right" philosophy may still be the best approach for dealing with obnoxious shoppers. Customer service experts have long said that a happy customer tells one or two friends, while an unhappy customer tells several--or in the age of social media, hundreds of his closest strangers. And these statistics can be magnified by the emotions related to holiday shopping.

"Businesses spend so much of their money acquiring customers, yet can lose them over one complaint," says Ken Varga, a marketing strategist in Spring Lake, N.J. After all, he adds, 99 percent of customers will obey the rules, so it's about appeasing that difficult 1 percent. So when someone returns a product beyond the 30-day money back window, for example, you're probably better off giving a refund with a smile. Otherwise, "they can hurt you badly," Varga says, especially by badmouthing you on Facebook and Twitter.

2. Train employees to cope with problem customers.
Donna Fluss advises her small-business clients to hold staff meetings between the end of October and Thanksgiving to do scenario training and discuss best practices for dealing with nightmare customers. "Give [employees] as many options as possible, especially in a season when people are short on time and short on money," says the founder of DMG Consulting in West Orange, N.J.

Staff members should be trained to be sensitive and make a reasonable effort to solve a customer's problem, Fluss says. "If a customer is over their credit limit, see if you can get them a one-time credit increase. Or if you know you can't get them a gift item in time for Christmas, suggest where else they may be able to find it, even if it's through a competitor."

3. Hire enough holiday help to minimize customer frustration.
Staffing up adequately during the holidays can prevent a lot of aggravation for both customers and employees. If someone is already upset and then has to wait a long time on line or on hold, this will only add fuel to the fire.

Overworked employees also may mishandle customers. If there aren't enough employees to deal with the increased holiday demand, Varga says, "the individual handling the disgruntled customer will try to rush, and as a result, the outcome won't be good."

4. Don't promise what you can't deliver.
You may want to appease an angry customer by promising to get a package delivered by Christmas Eve, but resist the temptation if the chances are slim. The last thing you want to do with a disgruntled shopper is make empty promises, says Esteban Kolsky, founder of thinkJar, a Kansas City, Kansas-based firm that focuses on customer service strategies.

"If you say you're going to try to do it and you don't do it, their problem becomes your problem," he says. "They don't use common sense, and then they expect the store or company to perform miracles. You always try to please your customer, but don't give them a reason to heap blame on you."

5. As a last resort, be willing to lose the customer and the sale.
If you offer your best plan for resolving a problem and the customer is still being difficult, it's okay to part company and refund the purchase price.

Your generosity of spirit should have limits, says Varga, whose rule is: Only one chance to break the rules per customer. "Times are going to get very tough and people will begin to make demands that are unrealistic just to see what they can get away with," he says.